there is already an ignore function:
/ignoreadd name (this will block you from being able to see anything someone says in chat, though they can still see you)
/ignoreremove name - removes them from ignore
/ignoreshow - will show you the full list of people on your ignore list
also a handy function to know, if mods are not around and someone is misbehaving use /report name reason this will then get the mods attention